The idea of “you don’t get paid but you get to split profits” is sound. It’s prevalent or underpins many industries from sales to books and movies or other art. But... the way this dude went about it is all wrong and shows you- as said by Nelson- in the first text that there’s a 99% chance dude is a joke.
Firstly- half? Of what? Gross? Net? Adjusted? App sales? In app purchases? Merchandising? Media rights? IP ownership? Half of what? Secondly- it’s very uncommon for a person with a brain to agree to work for (or offer..) a percent on return of a project you have no idea what it is. That’s what a pitch is. If your app idea is a sock organizer I’m out. I don’t see profit potential there or growth. If you pitch an idea for a novel and useful product I think could go places or be bought out by a bigger firm- I may be game.
But that’s another part of the pitch. Your angle. You’re going to make an app that allows people to see what certain outfits look like on them digitally, and can size the clothes for them? Sounds amazing. Do you have the algorithms and methods to accurately and conveniently get body measurements with a phone? Do you own that method- the IP? Who are you connected to? Has Victoria secret or Macy’s or Hugo Boss or GAP or anyone shown an interest? Do you golf with someone or have a friend who can set up an in to get a major partner on board, or at least some small online boutiques lined up?
Not only could that be a hit app if it worked- with potential to license the tech or sell it to a larger company; but the data itself on average human measurements and demographics, body shape, etc. etc- is worth money and a major company might buy you out just for all the data you’ve mined through your app.
The fact you have no pitch and approach the question like that indicate you don’t have any weight behind this, and you have no skin in the game. Offering 50% profit split to a single app developer also doesn’t look good. Why would you offer half- to one person- for a hit idea? What do negotiations look like when you offer 50% up front “I’ll take 60%?” Freaking clown shoes.
TLDR: While this type of deal may be profitable, this dude clearly doesn't operate at that level.